1. Field of Invention
The present invention relates generally to the field of optical devices. More specifically, the present invention is related to a beam directing device for directing beams of light to and from two optical waveguides encased in a single ferrule, which is coupled to an optical device via a single collimating lens.
2. Discussion of Related Art
Optical fiber (xe2x80x9cfiberxe2x80x9d) has been widely utilized as a transmission medium for telephony service providers for a number of years, as well as for metropolitan area networks (MAN) in many environments. In recent years, fiber has come into more widespread use in local loop plants, local area networks (LAN), in addition to finding an increased use at the edge of many networks. Further, fiber is expected to continue to penetrate many aspects of telecommunications, including many access-type networks, such as so-called fiber to the home (FTTH) and so-called fiber to the desktop (FTTPC).
The penetration of fiber continues because it advantageously provides for greater capacity and bandwidth. New services (e.g., Internet, high-speed data, video, audio, etc.) and the demands for these services, however, has significantly impacted bandwidth needs and has generated a desire for greater bandwidth capabilities than those available from legacy optical communications networks. Generally, there are two solutions to this increased bandwidth need. The first solution is to install more fiber to support the additional bandwidth. Depending upon the circumstances, however, this solution becomes cost prohibitive, and instead, the second solution of increasing the transportable bandwidth of existing fiber is pursued.
One method of increasing the transportable bandwidth of fiber is wavelength division multiplexing (WDM). WDM is an optical technology that combines two or more wavelengths of light, known as carriers or channels, for transmission along a single fiber. Each channel represents a bit stream that is carried over the corresponding wavelength, and different services or bit rates may be utilized for a given channel. This effectively increases the aggregate bandwidth of the fiber. For example, if 40 wavelengths, each capable of 10 Gb/s are used on a single fiber, the aggregate bandwidth of the fiber becomes 400 Gb/s.
There has additionally been another method of increasing transportable bandwidth, termed dense wavelength division multiplexing (DWDM). DWDM generally involves combining a denser number of wavelengths ( greater than 40) onto a fiber than WDM. While DWDM deals with more difficult issues associated with multiplexing a larger number of wavelengths on a fiber, such as cross-talk and non-linear effects, WDM and DWDM are typically used interchangeably.
Both of these technologies utilize optical devices based on the properties of light in both free space and in transparent materials. Examples of these devices include optical transmitters, optical receivers, optical filters, optical modulators, optical amplifiers, optical multiplexors/demultiplexors and optical circulators. To perform their functionality, many of these devices receive or output multiple, separate WDM beams via three or more different fibers. These fibers are coupled to the device through spatially separated input/output ports, which typically have optics for conditioning the optical beam prior to injection into the device. It is disadvantageous, however, to have spatially separated input/output ports for each fiber, as this increases the bulk of the device, when there is a desire for more compact devices. Yet, to provide the appropriate overall processing, these beams must be kept spatially separated during at least part of their processing, so as to be processed by some independent optical components of the device.
One such device that receives or outputs multiple, separate WDM beams via three or more different fibers is an interleaver/deinterleaver (xe2x80x9cinterleaverxe2x80x9d). An interleaver is a type of optical multiplexor which, when operating as an interleaver, combines subsets of channels from different fibers into a single optical beam. When operating as a deinterleaver, the interleaver separates a single optical beam having a series of channels into two or more subset series of channels. Typically, an interleaver is used to separate or combine even and odd International Telecommunications Union (ITU) channels.
FIG. 1 conceptually illustrates the function of an interleaver. When operating as an interleaver, the interleaver receives a first optical beam 100, which comprises a number of even channels at frequencies f2, f4, f6. The frequencies of each channel are such that each of these channels are separated by the same amount, e.g. 200 GHz. The interleaver also receives a second optical beam 102, which comprises a number of odd channels at frequencies f1, f3, f5. Similar to beam 100, the frequencies of each of these channels are such that these channels are separated by the same amount, e.g. 200 GHz. The even and odd channels, however, are offset from each other, normally an amount equal to half their separation distances, e.g. 100 GHz. The interleaver then interleaves the beams 100 and 102 to generate a beam 104 having with the channels f1, f2, f3, f4, f5, f6, which are separated by 100 GHz. When operated as a deinterleaver, beam 104 is received and divided into beams 100 and 102.
Various techniques have been developed to accomplish multiplexing and interleaving. For example, diffraction grating methods, utilize a series of parallel grooves to diffract different wavelengths of light at different angles (U.S. Pat. No. 4,643,519 to Bussard et al. (International Telephone and Telegraph Corporation, Feb. 17, 1987) and U.S. Pat. No. 4,744,618 to Mahlein (Siemens Aktiengesellschaft, May 17, 1988)). Arrays of planar waveguides (AWG) direct an input multi-wavelength beam into multiple curved waveguides. The waveguides have slightly different lengths, so that the light takes different times to pass through each waveguide (U.S. Pat. No. 5,414,548 to Tachikawa et al. (Nippon Telegraph and Telephone Corporation, May 9, 1995) and U.S. Pat. No. 5,841,919 to Akiba et al. (Hitachi Cable, Ltd., Nov. 24, 1998)). One method utilizes fiber gratings that are optical fibers in which the refractive index varies regularly along their length. The variations scatter light (Bragg effect), and a narrow range of wavelengths can be selected (U.S. Pat. No. 5,825,520 to Huber (Oct. 20, 1998)).
Another technique involves the use of optical birefringent elements. Birefringent materials differ from other transparent materials in that they have different indices of refraction in different directions. Thus ordinary and extraordinary rays travel at different velocities through the birefringent material. Use of such birefringent elements has been described in U.S. Pat. No. 4,566,761 to Carlsen et al. (GTE Laboratories Inc.) issued Jan. 28, 1986, and U.S. Pat. No. 4,685,773 issued Aug. 11, 1987, a continuation-in-part thereof. Carlsen et al. used a single birefringent element between two polarizing beam splitters to make a polarization insensitive wavelength multiplexer/demultiplexer that is useful in fiber optic systems. They first split the input beam into two orthogonal plane polarized components that are passed in parallel through the birefringent element and then are recombined in the second polarizing beam splitter to provide two output beams consisting of the input light separated according to wavelength. This interleaver suffers from the disadvantage that it requires two spatially separated optical paths, and the output ports are perpendicular. This means that the interleaver will be bulky when a more compact size is desirable.
U.S. Pat. No. 5,694,233 to Wu et al. (Macro-Vision Communications, LLC) issued Dec. 2, 1997, describes a switchable wavelength device which functions both as a router and as a demultiplexer. A router is a device that spatially separates input optical channels into output ports and permutes these channels according to control beams to a desired coupling between an input channel and an output port. The device described has a series of birefringent elements, polarization rotators, and wavelength filters which together function to split an incoming beam into divided optical beams comprising a subset of the channels and spatially positions the divided optical beams in response to a control beam applied to the router. In this case, the output ports are parallel. However, the output ports are spatially separated, meaning that the interleaver will be bulky. Such an interleaver will also be expensive, since the cost increases with the size and number of components.
Circulators are another example of a device that receives or outputs multiple, separate WDM beams via three or more different fibers, and which it is advantageous to not have spatially separate input/output ports for each fiber. Circulators are non-reciprocal optical devices that sequentially direct light from one port to another. For instance, in a three port circulator, light entering the first port leaves via the second port, however, light entering the second port does not leave via the first port, but rather, leaves via a third port. In closed circulators light entering the third port leaves via the first port, while in open circulators, light entering the third port is extinguished within the circulator. Examples of circulators known in the art are described in U.S. Pat. No. 5,909,310 to Li et al. (Jun. 1, 1999) and U.S. Pat. No. 5,930,039 to Li et al. (Jul. 27, 1999).
A more compact three-port optical circulator is described in U.S. Pat. Nos. 5,909,310 and 5,930,039. The optical circulator is made more compact by allowing a single lens to be used for collimating the light from the first and third fibers. A single lens can be used because the light coupled to the first and third fibers is not parallel; rather there is a slight angle between the two beams. A polarization dependent light-bending device is then used to compensate for the angle between the beams. While Li et al. allow for a more compact three-port circulator, the manner in which the polarization dependent light-bending device is used does not provide for a four-port circulator. Furthermore, Li et al. do not teach the use of the polarization light-bending device in a manner providing for a more compact interleaver/deinterleaver.
Whatever the precise merits, features and advantages of the above cited references, none of them achieve or fulfills the purposes of the present invention.
Accordingly, the present invention relates to an optical component for directing signals between a first port and a first path, and for directing signals between a second port and a second path, wherein the first and second paths are parallel, and wherein the first and second ports are positioned between said first and second paths, the optical component comprising:
a first port for inputting and outputting optical signals;
a second port for inputting and outputting optical signals;
a first lens for collimating incoming signals from the first and second ports and for launching them along diverging third and fourth paths, respectively; and for receiving outgoing optical signals traveling along the third and fourth paths and focusing them onto the first and second ports, respectively;
first polarization dependent beam deflecting means optically coupled to said first lens for directing optical signals with a first polarization traveling between the third path and the first path, and for directing optical signals with a second orthogonal polarization between the fourth path and the second path.